Master Post-Only Orders to Cut Your Trading Fees

Post-only orders represent a strategic tool that fundamentally changes how traders interact with the market. By definition, a post-only order guarantees that your limit order will only be placed into the order book rather than filled immediately against existing market orders. This distinction matters because it directly impacts your trading costs—orders that sit on the order book incur a lower maker fee, while orders that execute against existing liquidity incur a higher taker fee.

Why Traders Choose Post-Only Orders

The primary advantage centers on fee optimization. When you submit a limit order without the post-only protection, volatile market conditions can trigger unexpected market fills. Imagine you’re a scalp trader working with 100,000 BTCUSD contracts. You place a buy order at USD 9,000 when the best asking price shows 9,001. By the time your order reaches the system, the market has already moved to 8,995. Without post-only safeguards, the system automatically executes your limit order as a market order, filling your entire position from 8,995 up to your limit price of 9,000. This means you’ve inadvertently paid the taker fee instead of the maker fee you expected—a costly mistake for high-frequency and large-volume traders.

This feature is particularly valuable for traders who rely on precise fee structures. Whether you’re executing scalping strategies or managing substantial position sizes, understanding and controlling which fee tier you pay can significantly improve your bottom line over thousands of trades.

How Post-Only Orders Protect Against Slippage

The mechanics are straightforward: the post-only mechanism actively monitors whether your order would execute immediately upon submission. If the system detects that your limit order would fill right away (because market conditions have moved in your favor), it automatically cancels the order rather than allowing it to execute as a market taker.

This is critical in fast-moving markets. Returning to our scenario: when you enable post-only on your limit buy order at 9,000 and find that the market has dropped to 8,995, the system recognizes that your order would fill immediately. Instead of catching you off-guard with an unexpected taker execution, the post-only order simply cancels. You maintain complete control and avoid paying the higher taker fee.

Your trading account type and market determine your access to this feature. Post-only orders are available for spot trading through Unified Trading Accounts, and for perpetual and futures trading across both Standard Accounts and Unified Trading Accounts. This broad availability means most traders can implement this strategy.

Real-World Scenario: The Difference It Makes

Consider the practical impact on your trading economics. In our BTCUSD example, taker fees typically run 2-4 basis points higher than maker fees, depending on your account tier. On a 100,000 contract position, that fee difference alone could amount to hundreds of dollars per trade. Over a month of active trading, disabling post-only unintentionally and paying taker fees instead of maker fees could add up to thousands in unnecessary costs.

The execution behavior demonstrates why this matters. Without post-only protection: volatile market movement leads to unexpected market fill, resulting in an accidental taker fee. With post-only enabled: the same volatile movement triggers an automatic cancellation, preserving your original intention to add liquidity and earning the maker fee.

It’s worth noting that your Time-In-Force strategy works hand-in-hand with post-only settings. While post-only determines how your order behaves relative to the order book, your TIF choice (such as Good-Til-Canceled or Immediate-Or-Cancel) determines how long the system holds your order if it does enter the book. Together, these tools give you granular control over execution mechanics and fee optimization.